Method & apparatus for W-CDMA handoff searching

• US 6,744,747 B2
• Filed: 08/22/2001
• Issued: 06/01/2004
• Est. Priority Date: 08/22/2001
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Rao, Subramanya P.N., Subrahmanya, Parvathanathan, Shiu, Da-Shan
• Primary Examiner(s): Hsu, Alphus H.
• Assistant Examiner(s): Nguyen, Toan D.
• Application Number:
  US09/935,505
• Publication Number:
  US 20030039228A1
• Time in Patent Office: 1,014 Days
• Field of Search: 370/331, 370/335, 370/342, 370/350, 375/150, 375/152, 455/436, 455/442, 380/268, 380/270, 380/274
• US Class Current: 370/331
• CPC Class Codes: H04B 1/7083 Cell search, e.g. using a three-step approach
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04B 2201/70702 Intercell-related aspects
• CPC Class Codes: H04W 36/00 Hand-off or reselection arrangements
• CPC Class Codes: H04W 48/16 Discovering, processing access restriction or access information
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

Techniques for improved handoff searching in asynchronous systems, such as W-CDMA, are disclosed. In one aspect, a two-step search procedure is used when a list of neighbor codes is known. In the first step, a received signal is correlated with a slot timing code to locate on or more pilots and the slot boundaries associated therewith. In the second step, the received signal is correlated with each of the list of codes at the slot boundaries identified with pilots in the first step to identify the pilot code and the frame timing associated with each pilot. Various other aspects of the invention are also presented. These aspects have the benefit of decreasing search time, which translates to increased acquisition speed, higher quality signal transmission, increased data throughput, decreased power, and improved overall system capacity.

Claims

1. A method for searching comprising:

correlating a received signal with a slot timing code to locate one or more pilots and slot boundaries associated therewith;

performing a code test for each code of the list of codes, the code test comprising;

performing a slot test for each slot corresponding to the pilot, the slot test comprising correlating the received signal with the code for a duration at an offset corresponding to the slot to generate an energy value;

comparing each energy value to a threshold to determine if the code corresponds to the pilot;

using the code corresponding to an energy which exceeds the threshold as a scrambling code for demodulation; and

using the slot boundary corresponding to the energy which exceeds the threshold as the frame boundary for the scrambling code.

2. A method for searching comprising:

correlating a received signal with a slot timing code to locate one or more pilots and slot boundaries associated therewith;

correlating the received signal with the code for a duration at an offset corresponding to the slot to generate an energy value;

testing a window of offset hypotheses around the slot boundary, wherein for each offset hypothesis the received signal is correlated with the code for a duration to generate an energy values;

detecting the energy values corresponding to the offset hypotheses to locate one or more peaks;

comparing each of the peaks to a threshold to determine if the code corresponds to the pilot

for each peak which exceeds the threshold, using the corresponding code as a scrambling code for demodulation; and

for each peak which exceeds the threshold, using the corresponding slot boundary as the frame boundary for the scrambling code.

3. A method for searching comprising:

correlating a received signal with a slot timing code to locate one or more pilots and slot boundaries associated therewith;

correlating the received signal with the code for a duration at an offset corresponding to the slot to generate an energy vale;

testing a window of offset hypotheses around the slot boundary, wherein for each offset hypothesis the received signal is correlated with the code for a duration to generate an energy value;

detecting the energy values corresponding to the offset hypotheses to locate one or more peaks;

comparing each of the peaks to a threshold to determine if the code corresponds to the pilot; and

terminating the step of testing the window of offset hypotheses around the slot when a pre-determined number of peaks are detected above the threshold.

4. A method for searching comprising:

correlating a received signal with a slot timing code to locate one or more pilots and slot boundaries associated therewith;

correlating the received signal with the code for a duration at an offset corresponding to the slot to generate an energy vale;

testing a window of offset hypotheses around the slot boundary, wherein for each offset hypothesis the received signal is correlated with the code for a duration to generate an energy value;

detecting the energy values corresponding to the offset hypotheses to locate one or more peaks;

comparing each of the peaks to a threshold to determine if the code corresponds to the pilot; and

terminating the code test for the pilot when one or more peaks are detected above the threshold during the slot test.

5. A method for searching comprising:

correlating a received signal with a slot timing code to locate one or more pilots and slot boundaries associated therewith;

correlating the received signal with the code for a duration at an offset corresponding to the slot to generate an energy vale;

testing a window of offset hypotheses around the slot boundary, wherein for each offset hypothesis the received signal is correlated with the code for a duration to generate an energy value;

detecting the energy values corresponding to the offset hypotheses to locate one or more peaks;

comparing each of the peaks to a threshold to determine if the code corresponds to the pilot; and

terminating the pilot test of a pilot when one or more peaks are detected above threshold during the code test.

6. A method for searching comprising:

correlating a received signal with a slot timing code to locate one or more pilots and slot boundaries associated therewith;

correlating the received signal with the code for a duration at an offset corresponding to the slot to generate an energy vale;

testing a window of offset hypotheses around the slot boundary, wherein for each offset hypothesis the received signal is correlated with the code for a duration to generate an energy value;

detecting the energy values corresponding to the offset hypotheses to locate one or more peaks;

removing the code from the list of codes for subsequent pilot tests when one or more peaks are detected above the threshold during the code test.